Cleanup crews wearing ventilators and hazardous-materials protective suits were seen entering and emerging from the building overnight and into early Thursday morning.

Police say two men face charges, though a police spokesperson was not able to provide details.

People who work in the building have been told it will remain closed until the evening, at the earliest, while police continue their investigation.

"The lab is being taken apart slowly and methodically because of the volatile nature of the chemicals involved," Sgt. Matt Small of Peel Regional Police told CBC News. "It won't be until 6 p.m. tonight until the lab is fully dismantled and the area is safe."